Effects of pH and bicarbonate on the nutrient status and growth of three Lupinus species

Aims: High pH, and high bicarbonate (HCO ₃ ⁻ ) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO ₃ ⁻ ] and high pH. Methods: We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8 ^a (adjusted by KOH), and 8 ^b (adjusted by KHCO ₃ ). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis. Results: Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8 ^a , all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8 ^b . High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P]. Conclusions: Lupinus angustifolius and L. cosentinii were sensitive to high [HCO ₃ ⁻ ] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO ₃ ⁻ ] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants.